稀释空气孔
燃烧效率
27．大多数燃气涡轮发动机在海平面起飞状态下燃烧效率几乎是100％，在高空巡航状态降低98％。如图4-10所示。
31．点火过程有贫油和富油极限，类似于图4-1l中表示稳定性的极限。然而，点火包线在稳定包线以内，因为在冷状态下建立燃烧比保持正常燃烧要困难得多。
排放尾气
32．在排气中发现的不希望有的污染物是在燃烧室中产生的。有4种主要污染物是受法规控制的。它们是未燃烧的碳氢化合物(未燃烧的燃油)、烟(碳粒)、一氧化碳和氮的氧化物。影响污染物生成的主要条件是压力、温度和时间。
Combustion chambers
正常状态
燃烧效率
Combustion stability
28.
Combustion stability means smooth burning and the ability of the flame to remain alight over a wide operating range.
29.
For any particular type of combustion chamber there is both a rich and weak limit to the air/fuel ratio, beyond which the flame is extinguished. An extinction is most likely to occur in flight during a glide or dive with the engine idling, when there is a high airflow and only a small fuel flow, i.e. a very weak mixture strength.
30.
The range of air/fuel ratio between the rich and weak limits is reduced with an increase of air velocity, and if the air mass flow is increased beyond a certain value, flame extinction occurs. A typical stability loop is illustrated in fig. 4-11. The operating range defined by the stability loop must obviously cover the air/fuel ratios and mass flow of the combustion chamber.
31. The ignition process has weak and rich limits similar to those shown for stability in fig. 4-11. The ignition loop, however, lies within the stability loop since it is more difficult to establish combustion under 'cold' conditions than to maintain normal burning. 33.在主燃烧区的富油区里，碳氢化合物转化成一氧化碳和烟。新鲜的稀释空气可用于在稀释区中将一氧化碳和烟氧化成无毒的二氧化碳。通过燃烧过程在稀释区的继续进行还能减少该区中未燃烧的碳氢化合物，以确保完全燃烧。
34．氮的氧化物是在和抑制其它污染物所要求的相同条件下形成的。因此，尽快地使火焰冷却下来并减少燃烧可用的时间是符合愿望的。这些相互冲突
的条件要求进行折衷，但是，燃烧室设计与性能的连续改善已经导致燃烧过程“清洁”得多了。
Emissions
32. The unwanted pollutants which are found in the exhaust gases are created within the combustion chamber. There are four main pollutants which are legislatively controlled; unburnt hydrocarbons (unburnt fuel), smoke (carbon particles), carbon monoxide and oxides of nitrogen. The principal conditions which affect the formation of pollutants are pressure, temperature and time. 材料
35．燃烧室包容壁及内部零件必须能够多承受主燃烧区中很高的燃气温度。实际上，通过采用现有的最好的耐热材料、耐高温涂层，以及用冷却火焰筒的内壁作为它与火焰的隔离层已经实现了上述要求。
33.
In the fuel rich regions of the primary zone, the hydrocarbons are converted into carbon monoxide and smoke, Fresh dilution air can be used to oxidize the carbon monoxide and smoke into non-toxic carbon dioxide within the dilution zone. Unburnt hydrocarbons can also be reduced in this zone by continuing the combustion process to ensure complete combustion.
34.
Oxides of nitrogen are formed under the same conditions as those required for the suppression of the other pollutants, Therefore it is desirable to cool the flame as quickly as possible and to reduce the time available for combustion. This conflict of conditions requires a compromise to be made, but continuing improvements in combustor design and performance has led to a substantially 'cleaner' combustion process.
点火包线
图4-10 燃烧效率随空气／燃油比的变化
ratio.
36．燃烧室还必须承受由燃烧产物造成的腐蚀、温
度梯度产生的蠕变失效和由振动应力产生的疲劳。
图4-11 燃烧稳定性极限
Fig. 4-11 Combustion stability limits.
MATERIALS
35.
The containing walls and internal parts of the combustion chamber must be capable of resisting the very high gas temperature in the primary zone. In practice, this is achieved by using the best heat-resisting materials available, the use of high heat resistant coatings and by cooling the inner wall of the flame tube as an insulation from the flame.
36.
The combustion chamber must also withstand corrosion due to the products of the combustion, creep failure due to temperature gradients and fatigue due to vibrational stresses.
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